Electrochemical Impedance Spectroscopy of Electrospun La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ Nanorod Cathodes for Intermediate Temperature – Solid Oxide Fuel Cells

Electrospun La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF) nanorod cathodes are investigated. Morphological characterization shows that the nanorods are arranged into a 3-D stochastic structure, with multiple contact points with each other. Experimental characterization of symmetrical button cells through electrochemical impedance spectroscopy demonstrates an electrode polarization resistance Rp = 3.9 Ω cm² at 940 K and Rp = 10.9 Ω cm² at 890 K. The impedance results, measured from 890 K up to 1,200 K, show that the depressed Gerischer behavior is not an intrinsic feature of the electrode, since it appears only at certain well defined temperatures, and then it tends to disappear for other operating temperatures. Equivalent circuit model fitting is accomplished through the depressed Gerischer element, and also through an alternative circuit based on a normal Gerischer coupled to an RQ element. The superior fitting capability of the latter equivalent circuit is demonstrated. The latter circuit allows to assess separately the impedance contribution of the electrode bulk, associated to the Gerischer element, and of the electrode/electrolyte interface, associated to the RQ element. Both the related polarization resistances are larger with the electrospun LSCF 3-D random nanorod electrode, rather than with an electrospun LSCF electrode with unbroken nanofibers laying neatly in-plane over the electrolyte.